In electronic device development, particularly the device developed by students and hobbyists for experimental and learning purposes, it is necessary to build a mock-up sample of the device after the electronic circuit has been established. A plastic enclosure is employed for housing and supporting the circuit as well as externally operable electrical components such as switches, potentiometer, display meter, and numerical touch panel, etc., as shown in FIGS. 1 and 5. Such enclosure commonly consists of two mating rectangular casings in which the electronic circuit board is mounted in one casing and the other casing, having side and top panels would serve as a cover which is then mounted over the first casing to form a complete enclosure. Such enclosure is generally relatively small in physical size and yet it is necessary to form openings in its side panels and/or the top panel for mounting the externally operable electrical components. Due to the relatively small physical size of the enclosure, it is difficult to form the required openings because firstly it is difficult to mount the plastic casings securely for cutting the openings; secondly, that the plastic side walls would crack readily when the openings are being formed by cutting or sawing. In order to reduce the risk of cracking while cutting or sawing the opening in a wall panel, it is the common practice that an opening is formed by first marking the outline of the opening in the wall panel, and a series of small holes are then drilled along the marked outline as shown in FIGS. 3 and 7. Finally the remaining outline marking between the neighboring small holes are cut or sawed to form the opening required as shown in FIGS. 4 and 8. Such task of forming an opening in the plastic wall panels is time consuming and awkward to carry out and moreover it still does not eliminate the problem in the difficulty of maintaining the casing securely in place for the drilling and sawing operations; and most of all, the opening thus formed would inherently have an irregular edge, and the shape is only more or less similar to the marked outline. An electrical component may be loosely mounted in such irregular edge opening so that during operation of such loosely mounted electrical component, there may be movement of the electrical component, its electrical connection terminals and its electrical connection wire to cause a potential electrical and/or fire hazard. Moreover, the irregular edge would often be visible after the electrical component has been mounted therein so that it presents an objectionable crude appearance of the device. The irregular edge may be refined with extensive and time consuming filing and trimming; however, after filing and trimming, it often results in an opening larger than the marked outline.
Furthermore, the enclosure may not be re-used for a further project which may have different externally operable electrical components to be mounted on different positions of the side and top panels. Thus, the enclosure is not re-usable.